Premature Infant

A premature infant, also called a preterm infant, is a baby born before 37 weeks of pregnancy. Because the final weeks of pregnancy are a critical period for the maturation of the brain, lungs, digestive system, and other organs, babies born early may not yet be fully prepared for life outside the womb. The degree of prematurity varies widely, and the level of medical support a baby needs depends heavily on how early the birth occurred and how much the baby weighed at birth.

While many premature infants go on to develop normally with appropriate care, the earlier a baby is born, the greater the likelihood of short-term complications and, in some cases, long-term developmental concerns. Advances in neonatal intensive care over recent decades have significantly improved survival and outcomes, even for babies born at the edge of viability.

Prematurity is generally classified by gestational age at birth, and this classification helps guide the intensity of care a newborn requires.

Late preterm infants are born between 34 and 36 weeks of pregnancy and typically have the fewest complications among premature babies, though they may still struggle with feeding, temperature regulation, or mild jaundice. Moderately preterm infants are born between 32 and 34 weeks and often need a period of monitoring or support in a neonatal unit. Very preterm infants, born between 28 and 32 weeks, usually require more intensive respiratory and nutritional support. Extremely preterm infants, born before 28 weeks, face the highest risk of serious complications and generally require prolonged care in a neonatal intensive care unit (NICU).

The physical signs of prematurity become more pronounced the earlier a baby is born. A premature infant is often noticeably smaller than a full-term baby, with thin, translucent skin through which blood vessels may be visible, and comparatively little body fat. Fine, soft hair called lanugo may cover the shoulders, back, and face, and features such as the ears may appear soft and underdeveloped due to a lack of cartilage. Premature babies often have low muscle tone and limited spontaneous movement compared with full-term newborns, and they may have difficulty maintaining a stable body temperature. Breathing patterns can be irregular, with brief pauses in breathing known as apnea, and the baby's cry may be weak. Feeding difficulties are also common, since the coordination of sucking, swallowing, and breathing is not always fully developed at birth.

In many cases, the specific cause of premature birth cannot be identified. However, several factors are known to contribute to early delivery. Multiple pregnancies, such as twins or triplets, place additional physical demands on the uterus and are strongly associated with preterm birth. Certain chronic conditions in the pregnant mother, including diabetes, high blood pressure, and kidney or heart disease, can also lead to a medically necessary early delivery when continuing the pregnancy would pose risks to the mother or baby. Problems affecting the uterus, cervix, or placenta — such as an abnormally shaped uterus, a cervix that shortens or opens too early, or a placenta that separates from the uterine wall prematurely — can likewise trigger preterm labor. Infections during pregnancy, particularly of the urinary tract or reproductive organs, are another recognized contributor.

A history of previous preterm birth meaningfully increases the likelihood of a subsequent premature delivery, which is why women with this history are typically monitored more closely in future pregnancies. A short interval between pregnancies, generally less than six months from delivery to the next conception, has also been linked to higher preterm birth rates, making pregnancy spacing a factor that can be discussed with an obstetric care team. Chronic maternal health conditions such as diabetes and hypertension raise the risk because they can affect placental function or necessitate early delivery for safety. Smoking, alcohol use, and certain substance use during pregnancy are modifiable risk factors that are directly associated with preterm labor and can be addressed through counseling and support. Limited or delayed prenatal care is also associated with higher preterm birth rates, since it reduces the opportunity to identify and manage risk factors as they arise during pregnancy.

While not all premature births can be prevented, certain steps can meaningfully lower the risk. 

Regular prenatal visits allow a care team to monitor the health of both mother and baby and to identify early warning signs of preterm labor, such as regular contractions or changes in vaginal discharge. Managing chronic conditions like diabetes and high blood pressure before and during pregnancy helps reduce the likelihood of complications that could necessitate early delivery. Avoiding tobacco, alcohol, and non-prescribed substances during pregnancy is one of the most effective preventive measures available. For women with a prior preterm birth or a shortened cervix identified during pregnancy, a care team may recommend additional monitoring or specific medical interventions to help extend the pregnancy safely.